How to Treat Red Thread Disease in the Lawn

Learn how to identify, treat, and prevent this common lawn fungus.

The first time you see a red-pink patch in your lawn, you might think it’s just a trick of the light. However, a closer look reveals something different from your usual green grass. The cause is likely a common lawn disease called red thread, named for the reddish-pink, spiky threads that can cling to the grass blades.

Red thread has a unique look, but it doesn't have to ruin your lawn. We’ll show you how to identify it, get rid of it, and keep it from coming back.

How to Identify Red Thread

If you suspect you have red thread, look for these tell-tale signs, especially in the early morning when dew is still on the grass:

Irregular Patches: You’ll notice straw-colored patches of grass that are irregular in shape and range from 2 inches to 3 feet across.
Reddish-Pink Threads: The disease gets its name from the brittle, antler-like strands that extend from the tips of grass blades. These threads may appear darker red when the grass is wet and pinker when it's dry.
Cottony Growth: In some cases, you may see small, pink, cotton-candy-like or gelatinous strands on the grass blades.
Ragged Blades: Affected grass blades often look ragged and appear to be dying back from the tip.

What Causes Red Thread?

Red thread is caused by the fungus Laetisaria fuciformis. It thrives in cool, wet weather and prolonged overcast conditions, making it a very common disease in the spring. However, it can also appear in the fall and winter, and can even remain active through the mild, wet winters of the Pacific Northwest.

Besides weather, red thread is often a sign that your lawn is stressed. The biggest contributors are:

An Underfed Lawn: Lawns without enough nitrogen are more susceptible to red thread.
Improper Lawn Care: Poor maintenance habits, especially overwatering, can create the ideal humid conditions for red thread to develop.

Grass Types Commonly Affected by Red Thread

Cool-season grasses are usually more affected by red thread than warm-season grasses. Cool-season grass types most commonly affected include:

Bentgrass
Kentucky bluegrass (some varieties)
Fine fescues
Perennial ryegrass

However, warm-season grasses like bermudagrass and zoysiagrass can be susceptible to red thread if they are stressed or under-fed.

Your Best Defense: How to Prevent Red Thread

Since a primary cause of red thread is under-nourished grass, your first line of defense is a strong lawn care routine.

Feed Your Lawn Regularly. A well-fed lawn has the nitrogen and other nutrients it needs to combat disease. Help stregthen your lawn by feeding 4 times a year. If you’re not sure where to start, try a personalized Scotts® Lawn Care Plan.
Water Properly. Too much moisture encourages red thread, so only water when necessary and do it in the morning so the grass can dry during the day.
Mow Correctly. Keep your lawn mowed to the ideal height for your specific grass type.
Aerate if Needed. If your soil is compacted, aerating can improve drainage and airflow, making the lawn less inviting for fungi.

How to Treat Red Thread When It Appears

If red thread continues to be a problem, it’s time to treat it with a fungicide.

For Targeted Control: Use Scotts® DiseaseEX™ Lawn Fungicide to kill the active fungus and prevent it from spreading. This broad-spectrum product controls red thread and other diseases for up to 4 weeks. Be sure to follow all label directions.
To Feed and Prevent: For a 2-in-1 solution, apply Scotts® Turf Builder® Healthy Plus Lawn Food. It combines a fungicide with lawn food to control red thread while helping your lawn grow thick and green, making it better able to recover from stress.

How to Repair Your Lawn After Red Thread

After controlling the disease, red thread may leave some damaged spots behind.

For Bare Spots: The easiest way to fix small patches is with EZ Seed® Patch & Repair. Just pick the formula that best matches your grass type and apply it to the damaged spots.
For Thin Areas: If the damage is more widespread, thicken your entire lawn with the appropriate Turf Builder® Thick'R Lawn® product for your grass type.

Red thread may look strange, but it’s a clear sign your lawn needs a little help. By treating the disease and taking steps to improve your lawn’s health, you can get it to move from just surviving to truly thriving.